Remove reference to deleted file

webpack.serve.js

@@ -13,11 +13,6 @@ module.exports = merge(common, {
         new HTMLWebpackPlugin({
             title: 'Converse.js Dev',
             template: 'webpack.html'
-        }),
-        new HTMLWebpackPlugin({
-            filename: 'tests.html',
-            title: 'Converse.js Tests',
-            template: 'tests.html'
         })
     ],
 });